Meaning and differences between directly and substantially in issue and incidentally and collaterally in issue.
In every civil suit, there is a requirement that a matter shall be in issue. It is rather an essential element of a civil suit along with other elements such as a cause of action, the subject matter, the parties and the title. Until and unless these mainly six elements coexists there just can’t be a civil suit in their absence. Talking about the matter in issue, it is further classified into two kinds that are the matter directly and substantially in issue and the matter incidentally and collaterally in issue.
Before differentiating its kinds and understanding the meaning of matter in issue, it is important to understand the meaning of cause of action. Basically it means an existence of a legal right. But there must be a violation of such legal right and the plaintiff has to state his cause of action clearly to the court so that the court can understand that cause of action and conduct the suit on that basis. And therefore in every suit, the cause of action has to be either proved or disproved. It must be proved by the aggrieved plaintiff while disproved by the defendant and this can be done on basis of certain facts. Those facts which essentially go on to prove or disprove the cause of action will be called as the matter in issue. It means the rights litigated between the parties, i.e. the facts on which the right is claimed and the law applicable to the determination of that issue.
It is also observed that matter in issue can be an issue of fact or an issue of law or a mixed issue of fact and law. To understand the meaning of directly and substantially in issue and collaterally and incidentally an issue an example is sought. A gives two parts of land on rent to B for rent of Rs. 5,000. But B only pays Rs. 2,500. In a suit, B contends that he has used just one portion of the land. So we can deduce from this example that the facts which disprove A’s cause of action is the area which the B claims he has used. So the matter in issue for B is the area while for A, it will be rent. When the court will do fact finding of such area, such matter in issue, though not directly in issue, would be incidentally and collaterally in issue.
The word directly in issue means immediately and without intervention and such cannot be said to be directly in issue if the judgement stands whether such facts exists or not. It has to be based on facts and circumstances of each case. Whereas substantially means essentially. It can be deduced to the meaning that something which is merely short of certainty but indeed more than suspicious. It means something in effect though not in express terms. Both the terms become imminent in a case when the determination of them would affect the decision of a suit. It has been observed time and again that there exists no rule of universal application to determine such matter in issue and it differs fro case to case with respect to their facts and circumstances.
The matter directly and substantially in issue can be further classified into two kinds, matter actually in issue and matter constructively in issue. A matter is actually in issue when it is per se on the fact of records and the same suit is decided on the merits. The term constructive applies when a legal fiction is created  by the court that it might and ought to have been made a ground of attack or defence in a former suit. Explanation IV Section 11 by a deeming provision lays down that any matter which might and ought to have been made a ground of defence or attack in a former suit, but which has not been made a ground of attack or defence, shall be deemed to have been a matter directly and substantially in issue in such suit. This principle is called constructive res judicata.
The matter which is collaterally and incidentally in issue is the one from which no relief is claimed. The word incidental means in continuation of the same suit, whereas the term collateral means a fresh finding. These are basically two matters which moves parallel to the matters directly and substantially in issue and yet are ancillary and used in contradistinction to them. Therefore it refers to a matter in which no relief is claimed and yet is put in issue to enable the court to adjudicate the matter which is directly and substantially in issue.
The major difference, if drawn between the matters directly in issue and substantially in issue in order to operate res judicata is that a matter must have been directly and substantially in issue in a former suit and not merely collaterally or incidentally in issue. A remedy is sought from the former matter while the latter which is collateral or incidental is merely decided for the fact finding by the court. Therefore we seek a relief from direct and substantial matter in issue and nothing of that sort in case of the latter kind because if it is necessary to decide in order to grant relief to a plaintiff or to a defendant and the decision on such issue either way does not affect the final judgement. The final difference between both is that while res judicata will apply on that matter in issue which was directly and substantially in issue in a former suit, nothing as such would apply on that matter which was incidentally and collaterally in issue in a former suit. At the risk of repetition, all such questions of matter must be decided on the facts of each case, and as it has been appreciably observed in case of Isher Singh v. Sawran Singh, no “cut and dried” test can be laid down to determine such questions.
 Mathura Prasad v. Dossibai N.B. Jeejeebhoy AIR 1971 SC 2355
 Pandurang Ramchandra v. Shantibai Ramchandra AIR 1989 SC 2240
 Lonankutty v. Thomman AIR 1976 SC 1645
 Govt of the Province of Bombay v. Pestonji Ardeshir Wadia AIR 1949 PC 143
 Explanation IV Section 11
 Ishar Singh v. Sarwan Singh AIR 1965 SC 948